1. Field of the Invention
The present invention relates to an image forming apparatus which, in a horizontal or upright position, will develop an electrostatic latent image on a latent image carrier with a powdery developer.
2. Description of the Related Art
In image recording apparatuses, such as a copying machine, a printer and a facsimile, a latent image forming apparatus like an electrophotographic apparatus is used due to the popularity of image recording on normal sheets of paper.
Such an image forming apparatus forms an electrostatic latent image on a photosensitive drum or the like. Then, the electrostatic latent image on the photosensitive drum is developed with a powder developer to provide a visible image. The developed image on the photosensitive drum is then transferred on a sheet, and the sheet is then separated from the photosensitive drum. Thereafter, the developed image on the sheet is fixed.
In view of the recent office environment, it is desirable that the image forming apparatus be sited in any position. That is, the image forming apparatus should be designed to allow a user to freely select the way the apparatus is sited, upright siting for narrower site space or horizontal siting for shorter site space.
FIGS. 10A and 10B arc explanatory diagrams of prior arts.
Such an image forming apparatus will be described below as an electrophotographic printer. As shown in FIG. 10A, a precharger 91 uniformly charges the surface of a photosensitive drum 90, and an exposing unit 92 exposes the photosensitive drum 90 to a light image to form an electrostatic latent image thereon. A developing unit 93 is provided to develop the electrostatic latent image on the photosensitive drum 90. This developing unit 93 supplies a powder developer (e.g., one-component magnetic toners or a two-component developer) to the photosensitive drum 90 to develop the electrostatic latent image.
The developed image on the photosensitive drum 90 is transferred on a sheet that has been fed out from a sheet cassette 98. The sheet carrying the transferred image is fed to a fixing unit 96 where the developed image is fixed on the sheet. The photosensitive drum after image transfer is cleaned with a cleaner 95.
The powdery developer in the developing unit 93 has fluidity in the direction of gravity, so that gravity is a dominant factor in supplying the powdery developer. The image forming apparatus shown in FIG. 10A, which functions in a horizontal position, will carry out a stable developing operation in the horizontal position.
This type of image forming apparatus may be provided with a handle 97 as shown in FIG. 10A so that a user can carry and place it upright for storage. Such an image forming apparatus has been proposed in Japanese Unexamined Patent Publication No. 130345/1983 and Japanese Unexamined Utility Model Publication No. 184061/1985, for example. This image forming apparatus is so designed as to prevent the developer from falling off the developing unit 93 when the apparatus is placed upright, and this apparatus cannot function in that upright position.
There has been proposed an image forming apparatus which can operate in an upright position in order to reduce the space it should occupy, as shown in FIG. 10B (sec Japanese Unexamined Patent Publication No. 4-84176, for example.). In this type, a developing unit 93 for developing an electrostatic latent image on a photosensitive belt 90 will properly function in an upright position, but will not carry out a stable developing operation in a horizontal position.
Due to the recent popularity of image forming apparatuses, there is a demand that the apparatuses should function in any position desired by the users. For example, while the image forming apparatuses in a horizontal position would be stable and require shorter site space, the apparatuses in an upright position would require narrower site space to ensure effective use of the space on a desk or the like. This demand cannot be fulfilled by the conventional apparatuses which could function in either a horizontal position or an upright position.
If the apparatus shown in FIG. 10A is placed upright, the developer would come off of the developing unit, disabling the supply of the developer. If the apparatus shown in FIG. 10B is used in a horizontal position, the supply amount of the developer would vary, thus changing the image density.